A Modular Open Systems Approach (MOSA) is an integrated business and technical strategy to achieve competitive and affordable acquisition and sustainment over the system life cycle. In the development of Department of Defense (DoD) systems, MOSA is an acquisition and design strategy, consisting of a technical architectures, that adopts open standards and supports a modular, loosely coupled, and highly cohesive system structure. MOSA implies the use of a modular design, including system interfaces designed according to accepted standards with which conformance can be verified. MOSA can be employed in both defense and non-defense sectors by using a modular architecture and an open business model to add, modify, replace, and remove system components across the acquisition life cycle.

The MOSA ecosystem depends on active involvement by multiple stakeholders across the Department of Defense.

DoD can use MOSA to design systems with highly cohesive, loosely coupled, and severable modules that can be competed separately and acquired from independent vendors. DoD is actively pursuing MOSA in the life cycle activities of its Major Defense Acquisition Programs and Major Automated Information Systems, keeping pace with the rapid evolution in technology and threats that require faster cycle time for fielding and modifying warfighting capabilities.

A key enabler for MOSA is the adoption of an open business model, which requires doing business in a transparent manner and leveraging the collaborative innovation of numerous participants across the DoD enterprise. This permits sharing risk, maximizing reuse of assets, and reducing ownership cost. MOSA allows the Department to incrementally acquire warfighting capabilities, including systems, subsystems, software components, and services, with more flexibility, competition, and innovation.

MOSA Benefits

There is no single, magic bullet for implementing MOSA. The user must determine the desired outcomes up front to fully realize its benefits. DoD seeks five primary benefits of MOSA:

  1. Enhance competition
    • open architecture with severable modules, allowing components to be openly competed.
  2. Facilitate technology refresh
    • delivery of new capabilities or replacement technology without changing all components in the entire system.
  3. Incorporate innovation
    • operational flexibility to configure and reconfigure available assets to meet rapidly changing operational requirements.
  4. Enable cost savings/cost avoidance
    • reuse of technology, modules, and/or components from any supplier across the acquisition life cycle.
  5. Improve interoperability
    • allow severable software and hardware modules to be changed independently.
      • Defense Acquisition Guidebook 3–2.4.1, Modular Open Systems Approach (2017)

The benefits to MOSA implementations complement one another, and it is likely that a program will seek to configure the benefits to achieve the necessary outcome.


Working Groups

To further the use of MOSA in defense programs, DoD Engineering leads a collaborative Modular Open Systems Working Group (MOSWG), whose participants represent multiple segments of the defense engineering and acquisition community, including Program Executive Offices, Program Managers, engineering, and science and technology proponents. The MOSWG promotes modular open engineering principles through the Services and other agencies and can assist in advancing modular open practices.

As a resource for MOSA practitioners in Government, industry, and academia, DoD Engineering manages the Modular Open Systems Community of Practice (CoP) website, hosted by Defense Acquisition University (DAU). The CoP site is open to the public. Users with a DoD Common Access Card may register with DAU and contribute comments and other content to the site.

Modular Open Systems Working Group

Membership: Program Executive Officers, Program Managers, engineers, science and technology components.

MOSA Community of Practice

Membership: Government, industry, academia

Website: Visit www.dau.edu website

Tri-Service Tiger Team

Membership: DoD, Service Leads, and Industry partners

For more information or to participate in the MOSWG or MOSA CoP, click the button below to email the Engineering Team/MOSA.



Air Force Open Architecture Management Office


Modular Open Systems Approach Community of Practice


Training and Education Resources

CLE 019 (DAU): This course describes MOSA principles from a business and technical perspective. It provides program examples of successful MOSA implementation, as well as sources that can assist an organization in implementing MOSA. This course is designed to familiarize students with MOSA best practices throughout the life cycle.


The Tri-Service Tiger Team reviewed and updated the following definitions, which can be found in the DAU Glossary.


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Office of the Under Secretary of Defense,
Research and Engineering (USD(R&E))
The Pentagon, Washington, DC 20301